1. Field of the Invention
The present invention relates to a substrate handling method and apparatus, and an attractive force inspection method and apparatus utilized therewith, used in a state wherein an attractive force is generated between a substrate and a substrate holder when the substrate as an object to be processed is held on the substrate holder where various processing is performed, for example, during plasma processing utilized in thin film formation, micro-fabrication and the like in the manufacture of semiconductor devices, liquid crystal display panels, solar cells and the like.
2. Description of the Related Art
To enhance device functionality, and reduce the processing costs thereof, efforts have been energetically undertaken in recent years to make plasma processing apparatus more accurate and faster, and to handle larger diameter process objects, while reducing damage. Of these, control of substrate temperature to achieve inplane uniformity and precision is required in particular to achieve uniform film quality in a substrate during film growth, and to ensure dimensional precision in the dry etching utilized in micro-fabrication, respectively. Plasma processing apparatuses that make use of either a mechanical clamp or an electrostatic attraction electrode have begun to be used as means for controlling the substrate temperature.
As examples of conventional plasma processing apparatus, there are such type as disclosed in Japanese Laid-open Patent Application No. 63-72877, Japanese Laid-open Patent Application No. 02-7520, Japanese Laid-open Patent Application No. 03-102820, and Japanese Laid-open Patent Application No. 04-100257.
FIG. 2 shows a cross-sectional view of the reaction chamber of a plasma processing apparatus disclosed in Japanese Patent Laid-open No. 04-100257. In this plasma processing apparatus, a vacuum chamber 131 having a gas feeding means 140, gas inlet 140a, and an evacuating mechanism 141 is utilized as the plasma processing reaction chamber. A substrate 132 to be processed is placed on top of an electrostatic attraction electrode 133 provided inside the vacuum chamber 131, and this substrate 132 is electrostatically attracted by the electrostatic attraction electrode 133. This electrostatic attraction is performed by applying from a direct current power source 134 a positive voltage and a negative voltage, respectively, to a pair of electrodes inside the electrostatic attraction electrode 133. In this state, ordinary plasma processing is performed on the substrate 132 by evacuating the inside of the vacuum chamber 131 to achieve a predetermined vacuum state, introducing reactive gases, and applying voltage. Plasma processing involves the generation of a plasma gas inside the vacuum chamber 131 by applying a high-frequency voltage from a high-frequency power source 136, and includes sputtering for forming a thin film which corresponds to the plasma gas constituents, dry etching for forming a conductive pattern by using the plasma gas to selectively remove in accordance with a photoresist a conductive layer on a semiconductor wafer, and ashing for removing unnecessary photoresist subsequent to dry etching.
Following this type of plasma processing, an electric charge remains in the dielectric layer of the surface of the electrostatic attraction electrode 133 even when the direct current power source 134 is shut off, and in some cases, an electric charge remains in the substrate 132 if it is of dielectric properties. For this reason, the substrate 132 continues to be electrostatically attracted to the electrostatic attraction electrode 133, and even when pushed upward by a push-up mechanism 139, the substrate 132 either cannot be released from the electrostatic attraction electrode 133, or incurs damage.
Accordingly, in this apparatus, when plasma processing is complete, the polarity of the applied voltage from the direct current power source 134 to the electrostatic attraction electrode 133 is reversed by a switching mechanism 135, thereby canceling the residual electric charge of the electrostatic attraction electrode 133, following which the substrate 132 is pushed upward and released from the electrostatic attraction electrode 133 by the push-up mechanism 139 so that it can be transported to the next process. Thereafter, ultraviolet rays are irradiated through a piece of quartz glass 138 onto the dielectric layer of the surface of the electrostatic attraction electrode 133 from, for example, a mercury lamp, which is an ultraviolet light source 137, thereby ultimately removing the residual electric charge on the surface of this dielectric layer in preparation for the next substrate to undergo plasma processing.
Conversely, instead of the above-described charge removal, a charge removing plasma process can also be performed. As an example of this kind of processing, there is a method, in which the residual electric charge is reduced by gradually lowering the applied power.
However, with the system in which charge removal is performed by reversing the polarity of the applied direct current voltage to the electrostatic attraction electrode 133 following plasma processing, it is difficult to remove completely but not excessively the residual electric charge. Consequently, there are cases in which either a residual electric charge remains, or a reverse polarity charge is applied, and the substrate 132 remains electrostatically attracted as-is. In a state such as this, if the substrate 132 is pushed up by the push-up mechanism 139, there is the danger that the process substrate 132 will be damaged. Further, transport trouble, such as the inability to transport, bad transport attitude, droppage, and improper loading at the next process, can occur when the substrate 132 is transported to the next process, thus lowering reliability.
Conversely, with the charge removing plasma process, because data related to the electrostatic attractive force is not directly monitored, the plasma discharge duration is set to last somewhat longer, causing a drop in throughput efficiency. Moreover, with charge removing plasma processing which is performed inside the vacuum chamber, dust is generated from the vacuum chamber caused by micro-sputtering, and there occurs impurities contamination and dust generation from the electrode material, which also leads to reduced quality and reliability.
Furthermore, the above-described electrostatic attraction between the substrate 132 to be processed and the electrostatic attraction electrode 133, and the problems associated therewith, are also caused by the plasma gas generated by a plasma generating apparatus inside the vacuum chamber for performing plasma processing on the substrate 132.
An object of the present invention is to provide a substrate handling method and apparatus, and an attractive force inspection method and apparatus utilized therewith, by which a substrate can be gently pushed up and released at proper timing from a substrate holder in accordance with the residual state of an attractive force generated between the substrate holder and the substrate which is supported and processed on the substrate holder.